按照官方手册最小化安装完成后重启httpd服务失败，journalctl -ex查询显示错误信息如下：
Mar 13 12:25:24 controller python2[24903]: File "/usr/share/openstack-dashboard/openstack_dashboard/settings.py", line 29, i
Mar 13 12:25:24 controller python2[24903]: import horizon
Mar 13 12:25:24 controller python2[24903]: importError: No module named horizon
Mar 13 12:25:24 controller systemd[1]: httpd.service: control process exited, code=exited status=1
Mar 13 12:25:24 controller systemd[1]: Failed to start The Apache HTTP Server.
-- Subject: Unit httpd.service has failed
Mar 13 12:25:24 controller python2[24903]: File "/usr/share/openstack-dashboard/openstack_dashboard/settings.py", line 29, i
Mar 13 12:25:24 controller python2[24903]: import horizon
Mar 13 12:25:24 controller python2[24903]: importError: No module named horizon
Mar 13 12:25:24 controller systemd[1]: httpd.service: control process exited, code=exited status=1
Mar 13 12:25:24 controller systemd[1]: Failed to start The Apache HTTP Server.
-- Subject: Unit httpd.service has failed
应该是python没有找到horizon包。
检查dashboard安装目录，发现确实没有找到horizon包，显然是安装遗漏了horizon，需要自己从官方代码仓里面拷贝过来
操作方法供参考：
$ git clone https://git.openstack.org/openstack/horizon -b stable/train --depth=1
$ cd horizon
$ cp -rf ./horizon /usr/share/openstack-dashboard/
$ systemctl restart httpd
纠正后，此问题消失，如果还不行的话，就要参考另外一位大佬的帖子了：
易陆发现/bbs168x - BBS168xhttp://wwww.yunshb.cn/thread-1846-1-1.html，
官方dashboard安装指导书：
OpenStack Docs: Install and configure for Red Hat Enterprise Linux and CentOShttps://docs.openstack.org/horizon/stein/install/install-rdo.html
